In recent years, the spread of electronic devices, including digital electronic devices, using high frequency waves has been advanced and, among them, the spread of mobile communication devices using quasi-microwave bands or microwave bands has been remarkable. In those mobile communication devices represented by portable telephones, demands for reduction in size and weight are so great that high-density mounting of electronic components has become the greatest technical problem. Accordingly, since the electronic components, the printed wiring, the inter-module wiring, etc. which are mounted overcrowdedly, approach to each other extremely, and further since the speed-up of the signal processing speed is schemed, the inter-line coupling due to the electrostatic coupling and/or the electromagnetic coupling becomes large and interference due to radiant noise or the like is caused, so that not a few situations have occurred wherein normal operations of the devices are impeded.
Conventionally, against such so-called high-frequency electromagnetic interference, a measure has been mainly taken to apply a conductor shield.
However, since the conductor shield is an electromagnetic interference countermeasure utilizing reflection of electromagnetic waves due to impedance mismatch relative to the space, it can provide a shielding effect but has a drawback to promote the electromagnetic coupling due to reflection from an undesired radiation source. For solving such a drawback, it could be considered effective as a secondary electromagnetic interference countermeasure to use a magnetic loss of a magnetic body, that is, an imaginary part permeability .mu." so as to suppress the undesired radiation.
It has been known that the absorption efficiency of undesired radiation increases corresponding to a magnitude of .mu." in a frequency range where .mu."&gt;.mu.'. Accordingly, for obtaining a large magnetic loss at a microwave band, it is necessary to realize a characteristic where the real part permeability attenuates due to the magnetic resonance at a VHF band (30 MHz to 300 MHz), a quasi-microwave band (300 MHz to 3 GHz) or a low-frequency side of a microwave band (3 GHz to approximately 10 GHz).
Therefore, it is an object of the present invention to provide a composite magnetic body where the magnetic resonance appears in a range from VHF band to microwave band and, as a result, a magnetic loss at the microwave band is large (that is, an imaginary part permeability .mu." is large). It is another object to provide an electromagnetic interference suppressing body using such a composite magnetic body.